GPS is the "classic" western navigation system. Currently using 31 satellites (as of 2014), it provides accurate position of up to 8 meters with a 95% confidence limit (civilian accuracy) provided there is unobstructed view on at least 4 satellites from the network.

GLONASS: it's the Russian equivalent of GPS, currently offering 24 satellites with global coverage (should have been 30, but 6 were lost at launch time in two separate incidents) as of 2014. Civilian accuracy of the GLONASS system is around 10 meters.

Beidou: the Chinese equivalent of GPS. Beidou currently offers 15 satellites with stable coverage of the Northern Hemisphere. The commercial accuracy is 10 meters.